Arsenal fear they will be without Kieran Tierney for the rest of the season, highlighting what Mikel Arteta feels is the “weakness” in their squad by meaning they have no fit specialist left-back in their bid to win the Europa League. Tierney suffered knee ligament damage in Saturday’s 3-0 defeat to Liverpool and will miss Thursday's Europa League quarter-final first leg against Slavia Prague. Arteta, who was counting the cost of their January dealings that leaves him without a natural deputy, is not sure if Tierney will feature for his club again this campaign and put his participation in Euro 2020, Scotland’s first major tournament for 23 years, in doubt. “It will depend on how things will evolve in the next few weeks,” he said. “He is keen to play for us again this season and extremely keen to represent his country in the Euros. We’re going to have to go day by day. “It looks like he doesn’t need knee surgery so the timeframe will be around [four-to-six weeks to return to training]. It could have been worse because the action looks scary but he’s feeling better and the damage is not that bad.” Tierney’s loss is a blow in two respects. The former Celtic player is a strong candidate to win Arsenal’s player of the year award, while they allowed his understudy, Sead Kolasinac, to join Schalke. Ainsley Maitland-Niles, who had played at both left-back and left wing-back for Arteta, also joined West Bromwich Albion in January and neither was replaced. Arteta accepted he was left short-staffed, adding: “We could not do anything on that window. We decided to let Kolasinac out on loan. We knew that that position was a weakness around the squad because we didn’t have anybody to replace him [Tierney].” Either Cedric Soares, a right-back by trade, or the versatile Bukayo Saka is likely to deputise for Tierney. While Arteta has used Saka as a left wing-back at times, he has not started in a back four this season and has been integral to Arsenal as a right winger. ________________________________________________ ________________________________________________ But by moving Saka, Arteta admitted they may have to change the way they play. He added: “We’re going to have to make some adjustments because his qualities are unique and we don’t have anybody to replace these qualities unless we start to move a lot of pieces. Without any time to train that’s a little bit dangerous to do. You have to find a different way of attacking and at the same time the structure when you are defending.” Arteta at least has the boost of Saka, Granit Xhaka and Emile Smith Rowe all back in contention after missing Saturday’s loss but David Luiz remains out and Martin Odegaard is a doubt, potentially costing them the services of another in-form player. Arteta said: “He’s been carrying an [ankle] injury for the last few days since he got injured with the national team.” Arteta described the performance against Liverpool as “unacceptable” but hoped it will be a blow that brings a response. “It was a big shock because of the trend before that,” he said. “Sometimes a punch in the face is good to come back to reality." Arsenal are 10th in the Premier League, 10 points behind fourth-place West Ham, meaning the Europa League offers their only likely route back into the Champions League. Arteta said: “We have to be realistic in the league and it’s difficult.” Winger Willian, who is one of many players who have been racially abused on social media, called for companies to stop allowing anonymous trolls to target people. “We have to find a way to change the profile of social media,” he said. “I think if people want to have Instagram, Twitter or Facebook [accounts], they need to put their IDs or passports or whatever. And then when these things happen the authorities can catch them. We have to try and find a way to stop it because when people say horrible words about you about your family that’s not good. We don’t see any action from the authorities. It’s a big problem and we want action.”